Once upon a time, when there seemed to be plenty of money and time, NASA would announce a plan to explore a certain planet of the Solar System and then solicit bids for spacecraft, operations and science investigations. That old way of doing business fostered missions that were very large in scope, carrying many instruments, involving large groups of people, taking many years to get organized and launched, and costing billions of dollars.

Nowadays, there's not as much money and time seems short, so there's a new way. The idea now is to launch many, smaller focused missions that can carry out a limited range of the most important science experiments with fast turn-around times. The entire cost of a mission – design, development, launch vehicle, instruments, spacecraft, launch, mission operations, and data analysis – is less than $299 million.

The philosophy of the Discovery series of missions is to solicit proposals for an entire mission from a consortia of industry, small businesses and universities. Former NASA Administrator Daniel Goldin called the Discovery spacecraft "faster, better, cheaper" planetary missions.

The new approach is an extreme departure from previous methods. It is NASA's attempt to streamline and downsize to meet the constraints of smaller post-Cold War budgets, while creating interplanetary probes capable of high quality U.S. science investigations. The faster, better, cheaper approach received criticism following loss of the Mars Climate Orbiter and Polar Lander spacecraft in 1999. On the other hand, NASA received applause for the NEAR, Mars Pathfinder, Lunar Prospector, and Stardust missions.

The first flight in the Discovery series was the Near Earth Asteroid Rendezvous (NEAR) mission to the Asteroid Eros. NEAR was launched February 17, 1996, the first spacecraft ever to rendezvous with, orbit around, and land on an asteroid. The Delta-2 rocket used to launch NEAR from Cape Canaveral Air Station was the smallest rocket ever used for a planetary mission. Along its journey to Eros, NEAR snapped unique photos of Earth, the Moon, Comet Hyakutake, and the Beehive and Pleiades star clusters. NEAR also paid the first visit to the carbon-rich C-type asteroid 253 Mathilde, taking several images there in 1997. NEAR arrived at Eros, 160 million miles from Earth, on Feb. 14, 2000. The asteroid was so far away that it took 15 minutes for NEAR's radio signal to travel to Earth. NEAR flew within 22 miles of the surface of the asteroid. Also known as Asteroid 433, Eros is big and close -- one of the largest near-Earth asteroids, with a mass thousands of times greater than other asteroids. Potato-shaped Eros is about 21 miles long, 8 miles wide and 8 miles thick. The number 433 means Eros was the 433rd asteroid to have its orbit calculated. The NEAR spacecraft, itself about the size of a small automobile, conducted the first long-term, close-up study of an asteroid. NEAR used imagers and spectrometers to analyze the nature of the asteroid. NEAR data confirmed that asteroid 433 Eros is a consolidated, primitive sample from the Solar System's beginnings. NEAR found the asteroid has craters, a 12-mile surface ridge, a density comparable to Earth's crust and a diverse surface makeup. The spacecraft saw square-shaped craters on Eros. While at Eros, NASA renamed the spacecraft NEAR-Shoemaker after the late space geologist, Gene Shoemaker. Then, after orbiting the space rock for a year, the NEAR-Shoemaker spacecraft landed on Eros in February 2001.
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Pathfinder
Launch: 1996
Target: planet Mars

Pathfinder Sojourner

The second Discovery mission to launch was Mars Pathfinder, which blasted off from Earth on December 4, 1996, to demonstrate a low cost method of delivering a set of science instruments and a Rover to the surface of Mars. With its Sojourner rover, the Pathfinder mission to Mars was a world-wide news event in 1997 because of its unique new landing system and the first-ever operation of a remote-control robot rover on the surface of the Red Planet. Pathfinder returned hundreds of images and thousands of measurements of the Martian environment.
LEARN MORE ABOUT MARS PATHFINDER[STO]LEARN MORE ABOUT MARS PATHFINDER[NASA JPL]

Lunar Prospector
Launch: 1998
Target: the Moon

The third Discovery mission was Lunar Prospector launched on January 6, 1998. Five days later, it successfully entered orbit 63 miles above the Moon's surface. Lunar Prospector was a mission for which scientists had waited since the Apollo astronauts last roamed the lunar surface in 1972. The science data returned from Lunar Prospector led scientists to create detailed maps of the gravity, magnetic properties and chemical composition of the Moon's entire surface. Prospector discovered deposits of ice just below the surface at both the north and south poles of the Moon.
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Stardust
Launch: 1999
Target: comet Wild 2

Stardust

The fourth Discovery mission was Stardust launched on February 7, 1999, the first spacecraft dedicated solely to studying a comet. When it reached Comet Wild 2 (pronounced "Vilt-2") in 2004, comet dust and interstellar dust particles were collected for the first time ever for return to Earth for analysis by scientists worldwide. On it's way to the comet, Stardust flew by Earth on January 15, 2001. At Comet Wild 2, the robot probe documented its ten-hour passage through the hailstorm of comet debris with science instruments and a navigation camera. As it approached the dust cloud, the spacecraft flippede open a particle catcher shaped like a tennis racket and filled with a smoke-colored glass foam called aerogel. After samples of particles flying off the nucleus of the comet were collected, the capturing device was folded down into a capsule for safe delivery to Earth. Stardust mission returned to Earth in January 2006 with the samples of comet dust. A parachute dropped the sample-return capsule onto a Utah desert salt flat.
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Genesis
Launch: 2001
Target: the Sun

Genesis

The fifth Discovery mission to be launched was Genesis. It blasted off August 8, 2001, on a million mile journey in the direction of the Sun. Scientists wanted to know what the Sun is made of and whether the Earth and planets are composed of the same materials. To find out, Genesis traveled to the so-called Lagrange L1 point in space a million miles from Earth. At that point, gravity of the Earth and the Sun are in balance. There, Genesis unfolded its ultra-high purity silicon collectors and "sunbathed" in orbit for more than two years, collecting pieces of the Sun from the solar wind, before returning to Earth with particles of solar wind on September 8, 2004. Arriving at Earth, Genesis' parachutes failed to open and the sample-return capsule plowed into the Utah desert. The debris was retrieved, however, and samples of the Sun were analyzed successfully in laboratories. The atomic and isotopic composition of the solar nebula and the planets, comets and asteroids were determined.
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CONTOUR
Launch: 2002
Target: comets Encke, Schwassmann-Wachmann

CONTOUR

The launch of the Comet Nucleus Tour (CONTOUR) in Summer 2002 was timed to encounter and study two or three different comets as they made their periodic visits to the inner region of our Solar System. At each comet flyby, CONTOUR was to have snapped high-resolution photos and collected samples for high-resolution analyses of the comet's composition, as well as determine the comet's precise orbit. The first encounter was to have been with Comet Encke in 2003. CONTOUR carried the same dust composition science gear as the earlier spacecraft Stardust, plus high resolution spectral imagers and a gas composition experiment. CONTOUR was launched July 3, 2002. Unfortunately, on August 15, when CONTOUR was to have fired its onboard motor to depart from Earth orbit, contact with the spacecraft was lost. The mission could not be retrieved. NASA said CONTOUR may have broken into pieces above Earth.
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Deep Impact
Launch: 2004
Target: comet Tempel 1

Deep Impact

Deep Impact was launched in December 2004 on a trip to the the Comet P/Tempel 1. As it flew by the comet, on July 4, 2005, it sent a hefty 770-lb. copper projectile bashing into the surface of that "dirty snowball" at more than 22,300 miles per hour. The crash created a spectacular football field-sized crater more than 65 feet deep. The entire comet was only four miles in diameter. The impact was the first attempt ever to peer beneath the surface of a comet to see freshly exposed pristine interior ice and rock. The new information about the ihe internal composition and structure of a comet revealed clues to the early formation of our Solar System. There will be no measurable change to the comet's orbit and no threat to distant Earth.
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Dawn
Launch: 2006
Target: asteroids Ceres and Vesta

If it had been launched to space in 2006, Dawn would have used a revolutionary ion-drive engine to push it along a nine-year course to study Ceres and Vesta, big boulders situated in the Asteroid Belt between Mars and Jupiter. Dawn would have flown within 62 to 500 miles of the surfaces of the asteroids. Ceres and Vesta have little in common except their size. Ceres, the largest known asteroid, has an older, more pristine surface, water-bearing minerals, and possibly a very weak atmosphere and frost. On the other hand, the dry surface of the brightest and third largest asteroid, Vesta, has been reshaped by basaltic lava flows. Vesta may have an early magma ocean like Earth's Moon. And, like the Moon, it has been hit many times by smaller space rocks. At least five times in the last 50 million years, those impacts have sent out lots of debris in the form of meteorites, which were recovered later on Earth. Dawn would have measured and reported to Earth the asteroids' physical attributes, such as shape, size, mass, craters and internal structure, and complex properties such as composition, density and magnetism. Unfortunately, after years of preparing for a June 2006 launch, NASA cancelled the Dawn mission in March 2006.
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Current Discovery Missions:ASPERA-3
Launch: 2003
Target: Mars

ASPERA-3

ASPERA-3, which stands for Analyzer of Space Plasma and Energetic Atoms, is what NASA refers to as a Discovery Mission of Opportunity. That means it is not a complete Discovery Mission, but rather merely one piece of a larger mission giving the U.S. scientific community a chance to participate in missions of non-U.S. government agencies by providing funding for a science instrument, hardware components of a science instrument, or expertise in critical areas of a mission. In this case, ASPERA-3 was one of seven science instruments aboard Mars Express, a European Space Agency probe launched from Russia on June 2, 2003. Along the way to Mars, ASPERA-3 studied the interaction between the solar wind and the Martian atmosphere. Mars Express arrived safely in orbit over Mars on December 25, 2003. From its orbit high above the planet, Mars Express is searching for water, ice and chemicals buried under the Martian surface. The various instruments onboard the orbiting platform will perform remote sensing measurements searching for answers to questions about the Martian atmosphere, and the planet's structure and geology. Mars Express also will drop a lander onto the Martian surface.
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MESSENGER
Launch: 2004
Target: planet Mercury

MESSENGER

Short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging, MESSENGER was launched March 3, 2004, to study the planet Mercury and provide the first global images of the Sun's closest neighbor. Mercury is the closest planet to the Sun. MESSENGER will enter orbit around Mercury in September 2009, after two flybys of Venus along the way. After performing the two Venus flybys, MESSENGER will make two flybys of Mercury in 2008 before settling into orbit around that innermost planet of the Solar System in 2009. MESSENGER then will orbit Mercury for at least one Earth year. Equipped with a camera, spectrometers, magnetometer and other instruments, MESSENGER will make the first detailed study of Mercury. The only other spacecraft to return data about Mercury was Mariner 10, which made three flybys of the planet in 1974 and 1975. Mariner 10 only imaged about half of the planet's surface. The multiple flybys of the Mercury will provide opportunities for global mapping and detailed characterization of the surface, interior, atmosphere, and magnetosphere. Understanding Mercury and the forces that have shaped it is fundamental to understanding the evolution of the four terrestrial planets, which also include Venus, Earth and Mars.
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Future Discovery Missions:Kepler
Launch: 2006
Target: exoplanets

Kepler

The Kepler space telescope will be an orbiting observatory gazing out across many lightyears at a region of deep space with tens of thousands of stars. It will search for Earth-like planets around stars beyond our own Solar System. Astronomers think it may find hundreds. Already astronomers indirectly have identified more than 80 of what are called exoplanets by observing their gravitational tug on their parent stars. However, that method has limited the search to planets comparable to or larger than the gas giants Jupiter and Saturn in our Solar System. Those Jupiter-sized planets around 300 times more massive than Earth. Operating in orbit above Earth, Kepler will watch a patch of 100,000 stars, looking for any sign of periodic dimming when planets pass in front of their parent stars. NASA says the Kepler observatory could identify the orbit and size of perhaps 500 planets, some comparable in size to Earth.
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NetLander
Launch: 2007
Target: planet Mars

NetLander

NetLander is another Discovery Mission of Opportunity for NASA. That means it is not a complete Discovery Mission, but rather one piece of a larger mission. NetLander is a European Mars exploration project, led by the French space agency Centre National d'Etudes Spatiales (CNES). Expected to take off from Earth in September 2007 on a European Ariane-5 rocket, NetLander will be composed of an orbiter and four identical landers on different parts of the Red Planet. When the NetLander orbiter is ten days out from Mars in August 2008, the four probes will be detached from it and dropped to the surface. They will land and unfurl their antennas, which will be used to communicate with the orbiter, which in turn will relay lander data to Earth. For more than a Martian year, the landers will measure conditions at their locations on the surface, meteorology, the planet's internal structure, and its magnetism.
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